The present invention generally relates to microwave and optical devices, and more specifically, to microwave-to-optical transducers.
Optical microcavities are known to confine light to a small volume. Devices using optical microcavities are today in many fields, ranging from optoelectronics to quantum information. Many types of optical cavities are known, such as Fabry-Perot-like cavities. The geometry (including thickness or width) of the cavity determines the “cavity modes”, i.e., particular electromagnetic field patterns formed by light confined in the cavity. An ideal cavity would confine light indefinitely (that is, without loss). The deviations from this ideal paradigm are either intentional (e.g., outcoupling) or due to design related limitations, fabrication related limitations, or imperfections (e.g., scattering). They are captured by the quality factor Q, which is proportional to the confinement time in units of the optical period. Another descriptive parameter is the effective mode volume (V), which relates to the spatial extent of the optical mode present in the cavity. In general, the realization of practical devices requires maximizing the ratio Q/V, i.e., high values for Q and low values for V are important to increase light-matter interactions in processes such as spontaneous emission, nonlinear optical processes and strong coupling.
Photonic crystals are natural or artificial structures with periodic modulation of the refractive index. Depending on the geometry of their structure, photonic crystals can be categorized as one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) structures. In one-dimensional photonic crystals, the periodic modulation of the permittivity occurs in one direction only. Well-known examples of photonic crystals are Bragg gratings, commonly used as distributed reflectors in vertical cavity surface emitting lasers. Quasi one-dimensional photonic crystal cavities are known, e.g., comprising a freestanding cavity that comprises periodic holes and a defect at the center. The central defect may for instance comprise tapered subsets of holes. For example, a concept for a photonic crystal nanobeam cavity has been proposed in J. Bochmann, A. Vainsencher, D. D. Awschalom and A. N. Cleland, “Nanomechanical Coupling between microwave and optical photons”, Nat. Phys. 9, 712 (2013), in which electrodes are directly attached to the nanobeam.
Cavity optomechanical systems are sometimes used in quantum information processing applications. Recent advances in quantum computing are making such a technology ever more relevant to industrial applications. Quantum computing makes direct use of quantum-mechanical phenomena, such as superposition and entanglement to perform operations on entangled quantum bits (qubits), i.e., information stored in quantum states. Superconducting circuits are relatively easy to manufacture with current technologies and are thus promising candidates to further scale quantum information technologies. Today, it can be envisioned that in the near term a small quantum computer, based on a couple of hundreds of superconducting qubits with limited to no error correction, will be able to simulate quantum systems intractable to conventional computers.